This invention relates to the recovery of a hazardous class of chemicals referred to as polychlorinated biphenyls. More particularly, the invention concerns the recovery of polychlorinated biphenyls from solution.
Compounds likely to accompany polychlorinated biphenyls in contaminated sites include polychlorinated alkylbiphenyls, polychlorinated polyalkylbiphenyls, polychlorinated triphenyls, polychlorinated oligo-phenyls, and polychlorinated polyphenyls, and metabolites of polychlorinated biphenyls, polychlorinated triphenyls, polychlorinated oligo-phenyls, and polychlorinated polyphenyls and others. The terms "PCB" and "polychlorinated biphenyls" as used herein are intended to be synonymous broad terms, including not only polychlorinated biphenyls themselves, but also related compounds which may accompany polychlorinated biphenyls in various processes or at contaminated sites.
PCB was known before the turn of the century. Although the useful industrial properties of mixtures obtained by chlorination of biphenyl were recognized early, PCB is relatively unreactive chemically. Therefore, from a purely chemical point of view, PCB is a rather uninteresting class of compounds. Limited attention was paid to them by the scientific community. However, in the mid 1960's, several publications noted the widespread occurrence of these compounds in the environment and the following events led to a dramatic upsurge of attention to PCB. It is now established that because of its lipid solubility (lipophilicity) and resistance to degradation, PCB accumulates in food chains and is distributed worldwide, like chlorinated pesticides such as DDT.
The literature on PCB is growing rapidly due to concern about PCB contamination of the environment. One result has been strict United States EPA standards on contamination. However, the removal of PCB from food chains is just one example of a broad need for methods of recovery of trace PCB contaminants from dilute aqueous and non-aqueous solution.
Prior art procedures for recovery of PCB include a variety of methods. One solution has been the reaction of PCB with hydroxylating agents. Unfortunately, such procedures are not always capable of effectively contacting and recovering PCB, especially when PCB is present only in trace quantities or in dilute solution. Furthermore, current PCB recovery strategies are expensive in terms of energy demand and time.
U.S. Pat. No. 4,619,744 teaches that heavy metals can be efficiently recovered from aqueous solutions by several novel methods involving interaction of the metals with water-soluble polymers. Unfortunately, the interactions between PCB and polymers are quite unlike those between heavy metals and polymers. Therefore, while a similar approach applicable to PCB was imagined at the time of the invention which led to U.S. Pat. No. 4,619,744, no such approach Was found by the inventors. This resulted in part from the extreme unreactivity of PCB. A contributing factor was the hydrophobicity of PCB. Polymers which are soluble in non-aqueous solvents and have functional groups capable of reacting with PCB have been difficult to find.